The Current and Future State of Optical Switching Technologies as Related to the Data Vortex Photonic Switching Architecture

The Data Vortex photonic packet switching architecture is designed to be a low-latency topology with minimal node complexity and a high degree of scalability [1,2]. The nodes from which this system is assembled require widebandwidth switching devices with very fast transitioning and minimal signal degradation. Semiconductor optical amplifiers (SOAs) have been selected as the most promising active component that fulfills these requirements for the Data Vortex as well as for the majority of other photonic packet switch fabrics [3]. In tracking switching technologies it is therefore critical to understand how the key physical parameters of the device compare with current commercial SOAs. Additional practical consideration such as the cost and power consumption are also important, and must be addressed. Issues concerning engineering feasibility, mechanical robustness, and reliability, and integratablility should be included in the overall analysis. (A recently-published general guide can be found in the literature [4].) The noise figure (NF) is perhaps the most important feature of a switching device. Measured in decibels (dB), this parameter describes the increase in the noise floor relative to the signal spectrum peak. Because these distortions are cumulative, the size of the Data Vortex network is ultimately limited by this figure [5]. Amplified spontaneous emissions (ASE) is the primary source of this broadband noise component in SOAs [6]. From fundamental quantum noise principals, it can be shown that the best possible amplifier noise figure of an optical amplifier is 3.0dB; typical real SOA noise figures range from 6 to about 8 dB. The operating current (also called “forward current”), generally on the order of 100 mA, relates directly to the total power consumption of the device, and also affects the switching speed in situ . This electrical current is the primary source of heat dissipation in the node since the SOA must remove the resulting ohmic heat, and since a current driver must be utilized to modulate this current at multi-gigahertz frequencies. While a higher operating current increases the gain of the device, it may also increase the noise figure. Furthermore, there is a minimum (or “transparency”) current at which the device begins to operate in a linear and well-behaved manner. The third major characteristic is the functional bandwidth of the device. Because the applications are designed to be wavelength-division multiplexed (WDM) at least across the whole ITU C-band (1528 nm to 1577 nm), it is necessary that devices operate almost linearly across the entirety of this spectrum. A Data Vortex switching node ideally requires less than 4.0 dB gain (see Fig. 1), and all commercially available amplifiers can deliver at least this much. So while gain is not a major concern, it is generally considered to be an important device specification. The domain over which the amplifier operates linearly is also important, but the maximum output power does not critically affect the present Data Vortex implementation.